Deforestation partly to blame for Queensland floods

Last week I sent a fairly random Tweet about deforestation in south-eastern Queensland being partially responsible for the record floods there. It went more or less unnoticed, but I thought the comment deserved a proper explanation.

Now, I will begin by saying I have no data yet to back up my Queensland-specific hypothesis, but I am contemplating a time-series paper on floods in Australia, especially after the events of the last month. This post is therefore merely a reasoned hypothesis.

The hypothesis itself is rather simple. Testing is not. I submit that the recent flooding in Australia has been exacerbated (not caused) by the rapid loss of forest cover over the last 40 years. We know that this is a particularly intense La Niña in Australia and our unusually high rainfall arises from this meteorological phenomenon, but I hypothesise that it wouldn’t have been as bad if this part of Australia hadn’t been so careless with its forest cover since the 1970s.

Figure 1

So what’s the evidence? Well, Queensland, especially south-eastern Queensland, has had some of the highest rates of forest loss since the 1970s. I trawled various government databases (data sourced from here and here) and discerned that not only did Queensland have the highest total forest loss between 1995 and 2005, it also had the highest proportional (i.e., relative to its area) forest loss since that time (Fig. 1).

Interestingly, this trend in proportional loss was maintained over the period 1995-2005 – Queensland had the sustained highest proportional (and absolute) rate of loss (Fig. 2).

Sure, most of you are familiar with the sad case of government-promoted land clearing in south-western Australia’s during the 1950s in the so-called ‘wheat belt’ which eventually gave rise to the dubious distinction of inclusion in the world’s Biodiversity Hotspots. Southern South Australia lost a good deal of its forest cover earlier, and New South Wales and Victoria have had a pretty poor history too (see David Lindenmayer‘s excellent book On Borrowed Time for the gory details). Nonetheless, it’s Queensland, and particularly the south-eastern section, which has copped the brunt of this cumulative wave of forest loss in our most recent history.

Figure 2

To support this contention, I pulled up the forest loss data for the Interim Biogeographic Regionalisation of Australia (IBRA) bioregions and mapped the net-loss regions from 1972-2004, 1980-2004, 1995-2004 and 2000-2004 (Fig. 3: increasing redness = increasing forest loss). As you can see, south-eastern Queensland (and some of northern New South Wales) has really been the epicentre of forest loss since the early 1970s (you can also so the legacy of loss in south-western Western Australia too in the earlier years – Fig. 3).

So I contend that the rapid deforestation and degradation of Queensland’s forests over the last few decades has destabilised the soil moisture regime to a point where it can no longer handle extreme weather events. This isn’t to say for a moment that these floods wouldn’t have happened if Queensland still retained all her forests – I hypothesise simply that they wouldn’t have been as severe.

Hi there there’s an interesting paper on fragmentation of vegetation from 1974 -1997 in the Lockyer valley which indicates why they had such an extreme event. Add pre 1974 clearing and post 1997 clearing and you have a system with a very different hydrological response

[…] me. But I definitly did know about alot of the environmental issues going on there – like the flooding in brisbane due to deforestation, the cane toad infestation (every single one of you should watch […]

Corey, I’m always fascinated how assiduously you can follow the causal chain but stop before
reaching anybody’s plate :). People don’t cut down forests and woodlands for fun.
They do it so that people who enjoy BBQs can use meat instead of veggie burgers. Or so they can export the meat to Japan and the US who will tut-tut about our deforestation over a steak. “Those damned silly QLD red (chomp) necks (chomp) cutting down their (chomp) forests and exacerbating their floods!” … the buck stops with the consumer.

Of course! We’ve disrupted the natural water cycle by deforesting and urbanising river catchments, so we can’t expect anything less. Floodplains hold an integral role in the Australian environment–disregarding their function simply creates problems for us.http://manuelinor.wordpress.com/2011/01/16/water-damage/

Couldn’t agree more. How about, if we spent some money on assuring that all catchments, from creeks to rivers, have a corridor of vegetation surrounding them. We will decrease overland flow, and increase infiltration. I’m just talking about a 20 m buffer zone or something similar. There are a million other benefits to doing this and I believe the money would be better spent then on building a more dams (Abbots solution).

If you do such a paper, you might also want to consider the impact of considerably historically high levels of overgrazing in WA’s Gascoyne-Murchison region, and any linkages to the recent flooding in Carnarvon…